During Phase Transformations

Many changes are taking place in our everyday lives, as we can observe when we glance about. The surface of an unattended glass of cold water becomes completely coated with liquid droplets after a period of time. Following the achievement of a specific temperature, when milk is held on a gas flame, bubbles begin to appear. When heated over a flame, a metal ring expands in diameter, water solidifies when kept in the freezer for an extended period of time, and ice cream melts when left out at room temperature. Has it ever occurred to you to ponder why these shifts occur? Phase Changes are the terms used to describe these modifications to the process (also known as Phase Transitions). Below, we’ll go over some of these transformations such as boiling, melting, and condensation.

Transition from one stage to another

Boiling

Boiled substances are those that have gone from their liquid phase to their gaseous phase as a result of the process of boiling. This procedure takes place when the temperature is raised to the boiling point or when the pressure is reduced to the atmospheric pressure, whichever occurs first. Among other things, it is used in cooking and water purification.

Condensation

It is the process by which a substance’s physical state transitions from its gaseous phase to its liquid phase that is called condensation. When water vapour comes into touch with a solid surface, it can also be defined as the transformation of water vapour into water drops. Separating a solute and solvent from a solution is a beneficial application of this procedure. Heat is applied to the solution, causing the solvent to evaporate, and the solvent is then separated and collected separately after the solution cools.

Heating a Metal: 

When metals are heated, their structural, magnetic, and electrical properties change. Upon heating, the metal enlarges. There is an increase in the length, the volume, and the surface area. Thermal expansion is the phrase used to describe the process of expanding material over time. Varying metals exhibit different degrees of thermal expansion. When developing metallic structures, such as domestic pipes and fittings, this approach comes in handy as a reference.

Frozen state: 

Freezing is the process by which a substance’s physical state changes from a state of liquid to that of solid. When the temperature of a liquid is decreased to the point where it reaches its freezing point, the process of phase transition occurs. This procedure is used in laboratories to preserve fruits and vegetables (frozen food) as well as animal specimens since it reduces the degradation and growth of microorganisms in the samples.

Melting

In science, melting is defined as the process of converting a substance from the solid to the liquid state. Thermal treatment causes this phase transition to occur by raising the temperature of the substance to the point where it melts (the melting point). Using this method, you can change the shape of any substance into another. Using metal blobs, for example, we can create rings and blocks in a variety of forms and sizes.

The change in enthalpy

In thermodynamics, the standard enthalpy of formation is the enthalpy of change, which has been determined for a large number of substances. When the reactants undergo chemical transformations and combine to form products, this is known as a general chemical reaction. It can be represented mathematically by the following formula:

In chemistry, enthalpy change is defined as the standard enthalpy of reaction.

The reaction enthalpy is the change in enthalpy that occurs as a result of any such reaction. It is denoted as rH in the equation. By subtracting the sum of all of the reactants’ enthalpies from that of the products, we may find out how much energy is involved in the reaction.

Mathematically,

ΔtH = Sum of enthalpies of the product in the system – Sum of the enthalpies of the reactants in the system

In chemistry, enthalpy change is defined as the standard enthalpy of reaction.

In this equation, the constants ai and bi denote the stoichiometric coefficients of the products and reactants, respectively, for the balanced chemical reaction that is being considered.

Standard enthalpy of reaction

In previous discussions, we learned that the enthalpy of every reaction is dependent on the physical characteristics of the surrounding environment, such as temperature or pressure. When calculating the standard enthalpy of a reaction, it is necessary to ensure that all of the components involved in the reaction, i.e., the reactants and the products, are in their standard forms; otherwise, the reaction will fail. Consequently, the standard enthalpy of reaction is the enthalpy change that takes place in a system when a substance is converted by a chemical reaction that takes place in a standard environment.

A material’s pure form at a pressure of one bar is considered to be the normal condition for any substance at a specific temperature according to conventional wisdom. For example, liquid ethanol at 298 degrees Celsius and 1 bar of pressure is said to be at its standard state when it is in its pure form. It is vital to remember that the data for a substance’s standard state is obtained at a temperature of 298 degrees Celsius. In chemical reactions, the standard enthalpy of a reaction is indicated by the symbol rHs. When it comes to consistency.

Conclusion

When dealing with a chemical process, understanding the concepts of enthalpy and standard enthalpy is extremely crucial. Calculating the temperature and pressure required for each chemical reaction is made easier with this tool. Also required when the reaction is carried out commercially (on a big scale), for example, when ammonia, calcium carbonate, oxygen, and other components are produced in considerable quantities. During this section, we will study about the computation of the change in enthalpy that takes place during a chemical reaction.